Arachnoid \A*rach"noid\, n.

1. (Anat.) The arachnoid membrane.

2. (Zo["o]l.) One of the Arachnoidea.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Arachnoid \A*rach"noid\, a. [Gr. ? like a cobweb; ? spider, spider's web + ? form.]

1. Resembling a spider's web; cobweblike.

2. (Anat.) Pertaining to a thin membrane of the brain and spinal cord, between the dura mater and pia mater.

3. (Bot.) Covered with, or composed of, soft, loose hairs or fibers, so as to resemble a cobweb; cobwebby.

Source: Webster's Revised Unabridged Dictionary (1913)